This invention relates to a system for integrally controlling an automatic transmission and an engine.
Automatic transmissions comprising gear transmission mechanisms, a plurality of frictionally engaging devices, and hydraulic pressure control devices operated to selectively switch the engagements of the frictionally engaging devices, so that any one of a plurality of gear stages can be achieved in accordance with a preset shift map, are well known in the transmission art.
Furthermore, in vehicle automatic transmission of the type described, various systems are known for integrally controlling an automatic transmission and an engine, wherein engine torque is changed during shifting to obtain satisfactory shift characteristics and durability of the frictionally engaging devices.
When the engine torque is changed during shifting, absorbed energy in the frictionally engaging devices for controlling members in the automatic transmission can be decreased. As a result, the shifting can be completed with low shocks for a short period of time, so that a satisfactory shift feeling can be given to a driver and the durability of the frictionally engaging devices can be improved.
However, in constructing the above-described system, when means for controlling the engine, means for controlling the automatic transmission and further control means for determining processing data including the engine torque change timing and engine torque change value are integrally provided, increased capacity of a computer leads to increased cost and it is disadvantageous to mount the system on a vehicle which has a high limitation in storage space.
Furthermore, adoption of the integrally controlling system may be disadvantageous from the viewpoints of all-around properties or common-purpose properties, because there are vehicles which require no engine torque control.
Now, when these control means are simply formed separately from each other, it is possible that advantages of expanded all-around properties to be obtained from forming these control means separately cannot be utilized so much, the subsequent development and improvement cannot be enhanced smoothly and/or disadvantages from a failsafe viewpoint are presented.
For example, in order to change the engine torque during shifting, it is inevitable to provide means for determining a timing and a change value for the torque change. In this case, the timing and the change value for the torque change should be varied in accordance with the progress of shifting, type of shifting, vehicle speed (shift point) and the like, and moreover, "gradual treatment" should be carried out when the engine torque returns from the changing. As a result, it is desirable to determine the timing and the change value on the side of the automatic transmission control means which grasps the state of shifting best. Incidentally, here, the "gradual treatment" means treatment that the engine torque is not to be abruptly changed in a stepped manner, but is to be gradually increased or decreased.
Further, in the case where the timing and the change value for the torque change are determined on the side of the automatic transmission control means, the determined information must be transmitted to the engine control means. In this case, when chronological changes of characteristics of requirements for the engine torque change are to be transmitted by analog signals, it is necessary to cause the engine control means to share special logic including A/D conversion. As a result, it is desirable to transmit the chronological changes by combination of a plurality of digital signals i.e., digital values. When the chronological changes are to be transmitted by the combination of the plurality of digital signals, the engine torque changes prearranged between the engine control means and the automatic transmission control means can be performed by the combinations of the signals.
However, if the relationship between the digital value and the engine torque change value are not suitably preset, then the engine torque change, particularly, the engine torque change during the gradual treatment is not performed as intended, and shift shocks may increase. For example, as disclosed in Japanese Patent Laid-Open (Kokai) No. 180768/1983, after the ignition timing is retarded by a predetermined angle during shifting to decrease the engine torque, even if the ignition timing is advanced by a little predetermined constant angle per ignition, the engine torque is not returned by degrees.